Electronic apparatus and transfer method

ABSTRACT

According to one embodiment, an electronic apparatus includes an interface circuit connectable to a first signal line, a second signal line, and a third signal line, and a controller. Before transmitting data using the first signal line, the controller is configured to transmit a first command using the first signal line while transmitting a first control signal using the second signal line, and transmit a first address using the first signal line while transmitting a second control signal using the third signal line. While transmitting the data using the first signal line, the controller is configured to transmit at least one of a second command and a second address using the second signal line and the third signal line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2020-156371, filed Sep. 17, 2020, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electronic apparatusthat transfers data and a transfer method.

BACKGROUND

An example of a storage device includes a solid-state drive (SSD). TheSSD includes a nonvolatile memory (for example, NAND flash memory) and amemory controller. The toggle interface is used as an interface betweenthe memory controller and the nonvolatile memory.

In the toggle interface, a command (and an address), and data aretransferred by an I/O signal line. The I/O signal line is shared forcommand (and address) transfer and data transfer. Therefore, it is notpossible to transfer the command (and the address) between the memorycontroller and the nonvolatile memory during the data transfer.Similarly, it is not possible to transfer the data during the command(and the address) transfer.

When a host transmits a read request or a write request to the SSDduring the data transfer, issuing of a command from the memorycontroller to the nonvolatile memory is delayed until the data transferis completed. A performance of the SSD is lowered by the latency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of amemory system including an electronic apparatus according to a firstembodiment.

FIG. 2 is a diagram illustrating an example of a configuration of a NANDchip.

FIG. 3 is a diagram illustrating an example of signal waveformsindicative of a write operation.

FIG. 4 is a diagram illustrating an example of signal waveformsindicative of a read operation.

FIG. 5 is a diagram illustrating an example of signal waveforms when awrite command and a read data command are sequentially issued.

FIG. 6 is a diagram illustrating a difference between a timing ofgenerating a read request and a timing of a read command.

FIG. 7 is a waveform diagram illustrating an example of a toggleinterface according to the embodiment.

FIG. 8 is a waveform diagram illustrating an example of serial transferaccording to the embodiment.

FIG. 9 is a diagram illustrating a state where four NAND chips arestacked and connected to a memory controller.

DETAILED DESCRIPTION

Hereinafter, an embodiment will be described with reference to thedrawings. The following descriptions are provided to exemplify a deviceand a method for embodying the technical idea of the embodiment. Thetechnical idea of the embodiment is not limited to a structure, shapes,arrangement, materials, and the like of components described below.Modifications easily conceivable by those skilled in the art arenaturally included in the scope of the disclosure. In order to make thedescriptions clearer, in the drawings, each element may be schematicallyexpressed by changing the size, the thickness, the planar dimension, theshape, or the like of the element from that in an actual embodiment. Indrawings, elements having different dimensional relations and differentratios may be included. In the drawings, corresponding elements may bedenoted by the same reference signs, and repetitive descriptions may beomitted. Although different names may be given to some elements, thenames are merely examples, and other names may be given to the elements.Other names are given to elements to which a single name is given. Inthe following description, “connection” means not only a directconnection, but also an indirect connection through another element.

In general, according to one embodiment, an electronic apparatusincludes an interface circuit connectable to a first signal line, asecond signal line, and a third signal line; and a controller configuredto transmit a first command, a first address, data, and one of a secondaddress and a second address via the interface circuit. Beforetransmitting the data using the first signal line, the controller isconfigured to transmit the first command using the first signal linewhile transmitting a first control signal using the second signal line,and transmit the first address using the first signal line whiletransmitting a second control signal using the third signal line. Whiletransmitting the data using the first signal line, the controller isconfigured to transmit at least one of the second command and the secondaddress using the second signal line and the third signal line.

FIG. 1 is a diagram illustrating an example of a configuration of amemory system including an electronic apparatus according to a firstembodiment. The memory system includes a host 12 and an SSD 14.

The host 12 is an information processing device configured to controlthe SSD 14. Examples of the host 12 include a personal computer, aserver computer, a portable terminal, and an onboard device.

The SSD 14 may be connected to the host 12 by a cable or via a network,or may be built in the host 12. The SSD 14 is a semiconductor storagedevice including a memory controller 20 and a nonvolatile memory 40.

An example of the nonvolatile memory 40 may be a NAND flash memory(referred to as a NAND memory hereinafter). The nonvolatile memory 40 isnot limited to the NAND memory. A NOR flash memory or other types ofnonvolatile memories may be used. The NAND memory 40 may have atwo-dimensional structure or a three-dimensional structure.

The NAND memory 40 includes a plurality of NAND chips. For example, theNAND memory 40 includes four NAND chips being a NAND chip (0) 42-0, aNAND chip (1) 42-1, a NAND chip (2) 42-2, and a NAND chip (3) 42-3. TheNAND chips 42-0 to 42-3 are collectively referred to as a NAND chip 42when it is not necessary to distinguish the NAND chips 42-0 to 42-3 fromeach other. Each of the NAND chips 42 includes a peripheral circuit 44and a plurality of planes. For example, each of the NAND chips 42includes two planes being a plane (0) 46-0 and a plane (1) 46-1. Theplanes 46-0 and 46-1 are collectively referred to as a plane 46 when itis not necessary to distinguish the planes 46-0 and 46-1 from eachother.

The SSD 14 may further include a random access memory, for example, adynamic random access memory (DRAM) 36. The DRAM 36 functions as abuffer for data transfer between the host 12 and the NAND memory 40. Aportion of a storage area of the DRAM 36 may be used as a write buffer,a read buffer, and a command buffer. The write buffer temporarily storesdata to be written to the NAND memory 40. The read buffer temporarilystores data read from the NAND memory 40. The command buffer temporarilystores a command received from the host 12 until the command isexecuted.

The memory controller 20 may be realized by a circuit such as a systemon a chip (SoC). The memory controller 20 includes a NAND interface(NAND I/F) circuit 32 that is electrically connected to the NAND memory40. The NAND I/F circuit 32 is a controller configured to control theNAND memory 40 under the control of a CPU 24. Therefore, the NAND I/Fcircuit 32 may also be referred to as a NAND controller. An example ofthe NAND I/F circuit 32 include a toggle interface.

Connection between the NAND I/F circuit 32 and the NAND memory 40 iscalled “channel”. The NAND I/F circuit may be connected to the NANDmemory 40 via a single channel or plural channels. The NAND memory 40may include a single NAND chip or plural NAND chips. In the embodimentof FIG. 1, the NAND I/F circuit 32 includes two channels. The NAND chips42-0 and 42-1 are connected to a first channel. The NAND chips 42-2 and42-3 are connected to a second channel.

The memory controller 20 may function as a flash translation layer (FTL)configured to perform data management and block management of the NANDmemory 40. The data management performed by the FTL includes: (1)management of mapping information indicative of the correspondencerelation between a logical address and a physical address of the NANDmemory 40; and (2) processing of hiding constraints (for example,read/write operation in units of pages and erase operation in units ofblocks) of the NAND memory 40.

In addition to the NAND I/F circuit 32 described above, the memorycontroller 20 includes a host interface (host I/F) circuit 22, a DRAMinterface (DRAM I/F) circuit 26, a static RAM (SRAM) 28, and anencoder/decoder 30. The host I/F circuit 22, the CPU 24, the NAND I/Fcircuit 32, the DRAM I/F circuit 26, the SRAM 28, and theencoder/decoder 30 are connected to each other via a bus 34. The memorycontroller 20 may be an integrated circuit in which the above-describedcomponents are mounted. Some of the above components may be providedoutside the memory controller 20.

The host I/F circuit 22 performs communication with the host 12.Examples of the host I/F circuit 22 include serial ATA (SATA), serialattached SCSI (SAS), PCI Express (PCIe)™, and Ethernet™. The host I/Fcircuit 22 receives various commands and various data such as a writecommand, write data, and a read command from the host 12. The writecommand includes a logical address (starting logical address) and thesize of write data. The write command instructs the SSD 14 to write thewrite data to the storage area of the NAND memory 40, which correspondsto the starting logical address and the size. The read command includesa logical address (starting logical address) and the size of data to beread. The read command instructs the SSD 14 to read the data from thestorage area of the NAND memory 40, which corresponds to the startinglogical address and the size.

The DRAM I/F circuit 26 is an interface circuit configured to controlthe DRAM 36 under the control of the CPU 24. The DRAM I/F circuit 26 mayalso be referred to as a DRAM controller.

The encoder/decoder 30 encodes and decodes data for error detection anderror correction in read data. The encoder/decoder 30 encodes write datato be written to the NAND memory 40. The encoder/decoder 30 decodes readdata read from the NAND memory 40. In decoding, the encoder/decoder 30performs error detection and error correction in the read data.

The CPU 24 is a processor configured to control the host I/F circuit 22,the NAND I/F circuit 32, the DRAM I/F circuit 26, the SRAM 28, and theencoder/decoder 30. In response to the power-on of the SSD 14, the CPU24 loads a control program (referred to as firmware) from the NANDmemory 40 or a ROM (not illustrated) into the DRAM 36, and executes thefirmware to execute various processes.

FIG. 2 illustrates an example of the configuration of each of the NANDchips 42. The peripheral circuit 44 in the NAND chip 42 includes aninput/output circuit 102, a logic control circuit 104, a chip controlcircuit 106, a command register 108, an address register 110, and aready/busy circuit 112. Each of the planes 46 in the NAND chip 42includes a memory cell array 120, a column decoder 122, a data register124, a sense amplifier 126, and a row decoder 128.

The channel CH connecting the NAND chip 42 and the NAND I/F circuit 32to each other includes I/O signal lines DQ [7:0] for transferring I/Osignals and control signal lines for transferring control signals. TheI/O signals include a command, an addresses, and data. The I/O signallines DQ [7:0] are connected to the input/output circuit 102.

The control signal lines include a chip enable signal line CEn, acommand latch enable signal line CLE, an address latch enable signalline ALE, a write enable signal line WEn, a read enable signal lineREn/RE, a data strobe signal line DQS/DQSn, and a ready/busy signal lineRY/BYn. A 1-bit control signal is transferred in each of the controlsignal lines. The command, the address, and the data are transferred inthe I/O signal lines DQ [7:0]. The command latch enable signal line CLEtransfers a command latch enable signal. The command latch enable signalindicates that the signals transferred by the I/O signal lines DQ [7:0]form a command. The address latch enable signal line ALE transfers anaddress latch enable signal. The address latch enable signal indicatesthat the signals transferred by the I/O signal lines DQ [7:0] form anaddress. The chip enable signal line CEn, the command latch enablesignal line CLE, the address latch enable signal line ALE, and the writeenable signal line WEn are connected to the logic control circuit 104.The read enable signal line REn/RE and the data strobe signal lineDQS/DQSn are connected to the input/output circuit 102. The ready/busysignal line RY/BYn is connected to the ready/busy circuit 112.

The signal transferred in the signal line includes a high active signal(positive logic signal) that is active (valid) at a high level or a lowactive signal (negative logic signal) that is active at a low level.Normally, a negative logic signal is represented by adding an overlineor an upper line to a symbol representing the signal. In thisspecification, for convenience of notation, the negative logic signal isrepresented by adding n after the symbol. For example, the chip enablesignal line CEn means transferring of a negative logic signal that has alow level when the NAND chip 42 is enabled and has a high level when theNAND chip is disabled. When the signal is at the valid level, the signalline is referred to as being “asserted”. When the signal is at theinvalid level, the signal line is referred to as being “deasserted”.When the signal line for transferring the positive logic signal isasserted, a signal level becomes the high level. When the signal linefor transferring the negative logic signal is asserted, the signal levelbecomes the low level.

Normally, the signal line is used for transferring a signal of eitherthe positive logic or the negative logic, but the read enable signalline REn/RE and the data strobe signal line DQS/DQSn are used fortransferring complementary signals of both logics.

The I/O signal lines DQ [7:0] are 8-bit signal lines for transferringdata, an address, and various commands. The NAND I/F circuit 32 assertsthe command latch enable signal line CLE when transferring a command bythe I/O signal lines DQ [7:0]. The NAND I/F circuit 32 asserts theaddress latch enable signal line ALE when transferring an address by theI/O signal lines DQ [7:0]. The NAND I/F circuit 32 transfers a commandand an address by the I/O signal lines DQ [7:0] in synchronization withthe rising edge of the write enable signal line WEn.

The NAND I/F circuit 32 transfers write data by the I/O signal lines DQ[7:0] in synchronization with both of the rising edge and the fallingedge of the data strobe signal line DQS/DQSn. The peripheral circuit 44transfers read data by the I/O signal lines DQ [7:0] in synchronizationwith both of the rising edge and the falling edge of the data strobesignal line DQS/DQSn.

The chip control circuit 106 causes a state transition based on variouscontrol signals received through the logic control circuit 104. The chipcontrol circuit 106 controls the operation of the NAND chip 42. Theready/busy circuit 112 transitions the state of the ready/busy signalline RY/BYn to a state between the ready state (RY) and the busy state(BY), under the control of the chip control circuit 106.

The input/output circuit 102 is a buffer circuit configured to transmitand receive the I/O signals to and from the NAND I/F circuit 32. Acommand, an address, and data latched by the input/output circuit 102based on an instruction from the logic control circuit 104 are stored inthe command register 108, the address register 110, and the dataregister 124, respectively.

The address stored in the address register 110 includes a chip number, arow address, and a column address. The chip number is identificationinformation for identifying the NAND chips 42. The chip number issupplied to the chip control circuit 106. The row address is supplied tothe row decoder 128. The column address is supplied to the columndecoder 122. The address may also include a plane number for identifyingthe plane. When the address does not include the plane number, anaddress space may be divided into sub-spaces of respective planes sothat the address can identify the plane. Similarly, the address may notinclude the chip number. In this case, the address space may be dividedinto sub-spaces of respective chips so that the address can identify thechip.

The logic control circuit 104 receives an input of the control signal.The logic control circuit 104 determines a register to which the I/Osignal received by the input/output circuit 102 is stored based on thereceived control signal. The logic control circuit 104 transfers thereceived control signal to the chip control circuit 106.

The memory cell array 120 in each of the planes 46 of the NAND chip 42includes a plurality of blocks. Each of the block includes a pluralityof pages. Each of the pages includes a plurality of memory cellsconnected to the same word line. The block is a unit of a data eraseoperation (also referred to as block erase) of erasing data from theNAND memory 40. The page is a unit of a data write operation and a dataread operation.

The column decoder 122 and the row decoder 128 specify the memory cellof the memory cell array 120 in accordance with the column address andthe row address. During the write operation, data in the data register124 is written to a memory cell specified by the column decoder 122 andthe row decoder 128. During the read operation, the sense amplifier 126reads data from a memory cell specified by the column decoder 122 andthe row decoder 128. The read data is written to the data register 124.

Next, the outline of the toggle interface between the memory controller20 (NAND I/F circuit 32) and the NAND memory 40 (peripheral circuit 44)will be described.

FIG. 3 illustrates an example of signal waveforms during the writeoperation. In an initial state, the chip enable signal line CEn is in adeasserted state, the data strobe signal line DQS/DQSn is in a highimpedance (Hi-z) state, and the states of other signal lines aredisregarded. The diagonal lines in FIG. 3 indicate that the state of thesignal line is disregarded.

The NAND I/F circuit 32 asserts the chip enable signal line CEn and thecommand latch enable signal line CLE, and deasserts the address latchenable signal line ALE, the write enable signal line WEn, and the readenable signal line REn/RE. The NAND I/F circuit 32 starts periodicasserting/deasserting of the write enable signal line WEn. That is, thelevel of the write enable signal line WEn periodically becomes the lowlevel and the high level. The NAND I/F circuit 32 sequentially transferscommands 01 h and 80 h to the NAND chip 42 by the I/O signal lines DQ[7:0] in synchronization with the rising edge (deasserting) of the writeenable signal line WEn. The input/output circuit 102 in the NAND chip 42sequentially latches the commands 01 h and 80 h which are sequentiallyinput by the I/O signal lines DQ [7:0], in synchronization with therising edge of the write enable signal line WEn.

The write mode of the NAND memory 40 is classified into several writemodes in accordance with how many bits of data can be written to amemory cell. Examples of the write mode include a Single Level Cell(SLC) write mode in which 1-bit data can be written to a memory cell, aMulti Level Cell (MLC) write mode in which 2-bit data can be written toa memory cell, a Triple Level Cell (TLC) write mode in which 3-bit datacan be written to a memory cell, and a Quad Level Cell (QLC) write modein which 4-bit data can be written to a memory cell.

Here, it is assumed that the write mode of the NAND memory 40 is the TLCwrite mode. Lower page data, middle page data, and upper page data,which are data for three pages, are written to a plurality of memorycells connected to the same word line. Since only data for one page iswritten in one write operation, the commands 01 h and 80 h are writecommands for writing the data of the lower page.

After transferring the command 80 h, the NAND I/F circuit 32 deassertsthe command latch enable signal line CLE and asserts the address latchenable signal line ALE.

The NAND I/F circuit 32 sequentially transfers column addresses C1 andC2 of two cycles and row addresses R1, R2, and R3 of three cycles to theNAND chip 42 by the I/O signal lines DQ [7:0] in synchronization withthe rising edge of the write enable signal line WEn. The input/outputcircuit 102 sequentially latches the column addresses and the rowaddresses which are sequentially input by the I/O signal lines DQ [7:0],in synchronization with the rising edge of the write enable signal lineWEn.

After transferring the row address R3, the NAND I/F circuit 32 maintainsthe deasserted state of the write enable signal line WEn to stop theperiodic asserting/deasserting of the write enable signal line WEn.

The NAND I/F circuit 32 deasserts the address latch enable signal lineALE after t_(CDQSS) from the start of transfer of row address R3.

The NAND I/F circuit 32 starts periodic deasserting/asserting of thedata strobe signal line DQS/DQSn. The NAND I/F circuit 32 sequentiallytransfers write data to the NAND chip 42 by the I/O signal lines DQ[7:0] in synchronization with both of the rising edge and the fallingedge of the data strobe signal line DQS/DQSn. The input/output circuit102 sequentially latches the write data which is sequentially input bythe I/O signal lines DQ [7:0], in synchronization with both of therising edge and the falling edge of the data strobe signal lineDQS/DQSn, and stores the write data therein.

After the transfer of the write data is completed, the NAND I/F circuit32 stops the periodic deasserting/asserting of the data strobe signalline DQS/DQSn.

The NAND I/F circuit 32 asserts the command latch enable signal line CLEand asserts/deasserts the write enable signal line WEn for only onecycle. The NAND I/F circuit 32 transfers a command 1Ah to the NAND chip42 by the I/O signal lines DQ [7:0] in synchronization with the risingedge (deasserting) of the write enable signal line WEn. The command 1Ahis indicative of the end of the write operation and the start oftransferring data latched in the input/output circuit 102 to the dataregister 124. The input/output circuit 102 latches the command 1Ah inputby the I/O signal lines DQ [7:0], in synchronization with the risingedge of the write enable signal line WEn.

FIG. 4 illustrates an example of signal waveforms during the readoperation where the write mode of the NAND memory 40 is the TLC writemode. The read operation includes a data output preparation operationand a data output operation. In the data output preparation operation,data is read from a memory cell specified by the address following theread data command, and the read data is written to the data register 124in the NAND chip 42. In the data output operation, the data in the dataregister 124 is transferred to the memory controller 20 by theinput/output circuit 102.

In the initial state, the chip enable signal line CEn is in thedeasserted state, the data strobe signal line DQS/DQSn is in the highimpedance (Hi-z) state, and the states of other signal lines aredisregarded. The diagonal lines in FIG. 4 indicate that the state of thesignal line is disregarded.

The NAND I/F circuit 32 asserts the chip enable signal line CEn and thecommand latch enable signal line CLE, deasserts the address latch enablesignal line ALE, the write enable signal line WEn/WE, and the readenable signal line REn/RE, and maintains the high impedance state of thedata strobe signal line DQS/DQSn.

The NAND I/F circuit 32 starts periodic asserting/deasserting of thewrite enable signal line WEn. That is, the level of the write enablesignal line WEn periodically becomes the low level and the high level.The NAND I/F circuit 32 sequentially transfers commands 01 h/02 h/03 hand 00 h indicative of the read data command to the NAND chip 42 by theI/O signal lines DQ [7:0] in synchronization with the rising edge(deasserting) of the write enable signal line WEn. The input/outputcircuit 102 sequentially latches the commands 01 h/02 h/03 h and 00 hwhich are sequentially input by the I/O signal lines DQ [7:0], insynchronization with the rising edge of the write enable signal lineWEn.

The command 01 h/02 h/03 h is indicative of a command for reading alower page, a middle page, or a higher page. The command 00 h indicatesthat the read address follows.

After transferring the command 00 h, the NAND I/F circuit 32 deassertsthe command latch enable signal line CLE and asserts the address latchenable signal line ALE.

The NAND I/F circuit 32 sequentially transfers column addresses ADD oftwo cycles and row addresses ADD of three cycles to the NAND chip 42 bythe I/O signal lines DQ [7:0] in synchronization with the rising edge(deasserting) of the write enable signal line WEn. The input/outputcircuit 102 sequentially latches the column addresses and the rowaddresses which are sequentially input by the I/O signal lines DQ [7:0],in synchronization with the rising edge of the write enable signal lineWEn.

After transferring the row address ADD, the NAND I/F circuit 32deasserts the address latch enable signal line ALE and asserts thecommand latch enable signal line CLE.

The NAND I/F circuit 32 transfers a command 30 h to the NAND chip 42 bythe I/O signal lines DQ [7:0] in synchronization with the rising edge ofthe write enable signal line WEn. The command 30 h instructs the NANDchip 42 of reading data from a memory cell specified by the addresswhich was previously input.

The input/output circuit 102 latches the command 30 h input by the I/Osignal lines DQ [7:0], in synchronization with the rising edge of thewrite enable signal line WEn.

When receiving the command 30 h, the NAND chip 42 starts reading of datafrom the memory cell array. The time taken to read the data is the timetR in FIG. 4. The time tR may be referred to as a preparation time tR.

After transferring the command 30 h, the NAND I/F circuit 32 maintainsthe states of the signal lines for the preparation time tR.

After the preparation time tR, the NAND I/F circuit 32 asserts thecommand latch enable signal line CLE and maintains the deasserted stateof the address latch enable signal line ALE.

The NAND I/F circuit 32 starts periodic asserting/deasserting of thewrite enable signal line WEn. The NAND I/F circuit 32 transfers acommand 05 h indicative of the start of a data output command, to theNAND chip 42 by the I/O signal lines DQ [7:0] in synchronization withthe rising edge (deasserting) of the write enable signal line WEn. Theinput/output circuit 102 latches the command 05 h input by the I/Osignal lines DQ [7:0], in synchronization with the rising edge of thewrite enable signal line WEn.

After transferring the command 05 h, the NAND I/F circuit 32 deassertsthe command latch enable signal line CLE and asserts the address latchenable signal line ALE.

The NAND I/F circuit 32 sequentially transfers column addresses ADD oftwo cycles and row addresses ADD of three cycles to the NAND chip 42 bythe I/O signal lines DQ [7:0], in synchronization with the rising edgeof the write enable signal line WEn. The input/output circuit 102sequentially latches the column addresses and the row addresses whichare sequentially input by the I/O signal lines DQ [7:0], insynchronization with the rising edge of the write enable signal lineWEn.

The NAND chip 42 start preparation of data transfer.

After transferring the row addresses ADD, the NAND I/F circuit 32deasserts the address latch enable signal line ALE and asserts thecommand latch enable signal line CLE. The NAND I/F circuit 32 transfersa command E0 h indicative of the start of a data output operation to theNAND chip 42 by the I/O signal lines DQ [7:0] in synchronization withthe rising edge of the write enable signal line WEn. The input/outputcircuit 102 latches the command E0 h input by the I/O signal lines DQ[7:0], in synchronization with the rising edge of the write enablesignal line WEn.

When receiving the command E0 h, the NAND chip 42 starts preparation ofdata output.

Then, the NAND I/F circuit 32 deasserts the command latch enable signalline CLE and maintains the deasserted state of the address latch enablesignal line ALE. The NAND I/F circuit 32 maintains the deasserted stateof the write enable signal line WEn to stop the periodicasserting/deasserting of the write enable signal line WEn.

The transfer direction of the I/O signal lines DQ [7:0] isbidirectional. During the transfer of the command, the transferdirection of the I/O signal lines DQ [7:0] is a direction from thememory controller 20 (NAND I/F circuit 32) to the NAND chip 42(input/output circuit 102). The NAND I/F circuit 32 drives the I/Osignal lines DQ [7:0] to transfer the command, and the input/outputcircuit 102 receives the command.

After t_(WHR2) from the stop of the periodic asserting/deasserting ofthe write enable signal line WEn, the NAND I/F circuit 32 deasserts theread enable signal line REn/RE and switches the transfer direction ofthe I/O signal lines DQ [7:0] to a direction from the NAND chip 42 tothe memory controller 20. After t_(WHR2) from the stop of the periodicasserting/deasserting of the write enable signal line Wen, theinput/output circuit 102 switches the transfer direction of the I/Osignal lines DQ [7:0] to the direction from the NAND chip 42 to thememory controller 20. Then, the input/output circuit 102 may drive theI/O signal lines DQ [7:0] to transfer data, and the NAND I/F circuit 32may receive the data.

When the switching of the transfer direction of the I/O signal lines DQ[7:0] is completed after t_(PREP) from the start of the switching of thetransfer direction, the NAND I/F circuit 32 starts periodicdeasserting/asserting of the read enable signal line REn/RE. Theinput/output circuit 102 starts periodic asserting/deasserting of thedata strobe signal line DQS/DQSn in conjunction with the periodicdeasserting/asserting of the read enable signal line REn/RE with a delayfor a predetermined time t_(DQSRE). Then, the input/output circuit 102transfers read data to the NAND I/F circuit 32 by the I/O signal linesDQ [7:0] in synchronization with the periodic asserting/deasserting ofthe data strobe signal line DQS/DQSn. The NAND I/F circuit 32 latchesthe read data input by the I/O signal lines DQ [7:0], in synchronizationwith the periodic deasserting/asserting of the data strobe signal lineDQS/DQSn.

When the number of the periodic deasserting/asserting of the read enablesignal line REn/RE reaches a predetermined number corresponding to thesize of the read data, the NAND I/F circuit 32 stops the periodicasserting/deasserting of the read enable signal line REn/RE. Thus, theperiodic deasserting/asserting of the data strobe signal line DQS/DQSnis also stopped. The NAND I/F circuit 32 deasserts the command latchenable signal line CLE and sets the data strobe signal line DQS/DQSn andthe I/O signal lines DQ [7:0] in the high impedance state.

In the toggle interface, a command and data are transferred by the I/Osignal lines DQ [7:0]. Therefore, it is not possible to transfer thecommand during data transfer. Similarly, it is not possible to transferthe data during command transfer.

When the plurality of NAND chips 42 are connected to each of thechannels of the memory controller 20, it is not possible to transfer thecommand to a NAND chip other than a target NAND chip to which the datais transferred, among the plurality of NAND chips connected to the samechannel.

FIG. 5 illustrates an example of signal waveforms when the write commandand the read data command are sequentially issued. The command 01 h isnot illustrated. FIG. 5 illustrates the signal waveforms between thememory controller 20 and the NAND chip 42-0. It is assumed that a readrequest is transferred from the host 12 to the SSD 14 at a time point t1when transfer of the write command from the memory controller 20 to theNAND chip 42-0 is completed. Then, the NAND I/F circuit 32 transfers thewrite data being the target of the write command, to the NAND chip 42-0by the I/O signal lines DQ [7:0]. Thus, it is not possible to transferthe read data command, immediately. After a time point t2 when transferof the write data to the NAND chip 42-0 by the I/O signal lines DQ [7:0]is completed, the NAND I/F circuit 32 can transfer the read data commandto the NAND chip 42-0 by the I/O signal lines DQ [7:0].

In the NAND memory 40, reading and writing are performed in page units.Thus, the maximum amount of data that can be transferred after transferof one command is the size of this page. The size of one page isoptional, but may be set to 17,336 bytes by adding ECC to data of 16kilobytes. A period for the data transfer of the page is a commandtransfer disabled period.

The command transfer disabled period depends on the data transfer speedof the toggle interface. For example, when the data transfer speed is4.8 Gbps (4.8 gigabits per second), the command transfer disabled periodis 3.96 μs. When the data transfer speed is 2.4 Gbps (2.4 gigabits persecond), the command transfer disabled period is 7.57 μs. When the datatransfer speed is 1.2 Gbps (1.2 gigabits per second), the commandtransfer disabled period is 14.80μs.

As illustrated in FIG. 4, during the read operation, the NAND I/Fcircuit 32 transfers the read data command. When the read data is storedin the data register 124 and the data output is ready, the NAND I/Fcircuit 32 transfers the data output command and receives the read datatransferred from the input/output circuit 102. The performance of theNAND memory 40 is lowered by the preparation time tR from the completionof the transfer of the read data command to the start of transfer of thedata output command.

Further, when there is the command transfer disabled period, issuing ofthe read data command is more delayed, and the performance of the NANDmemory 40 is more lowered. FIG. 6 is a diagram for explaining thepreparation time tR for outputting the read data and the commandtransfer disabled period.

FIG. 6 illustrates the state of the I/O signal lines DQ [7:0] when theread operation is executed after the write operation. It is assumed thata read request is issued after the NAND I/F circuit 32 transfers thewrite command to the NAND chip 42 and before the NAND I/F circuit 32transfers the write data. Since the period for transferring the writedata is the command transfer disabled period, there is a latency fortransfer of the read data command. When the transfer of the write datais completed, the NAND I/F circuit 32 transfers the read data command tothe NAND chip 42. Then, when the preparation time tR elapses, the NANDI/F circuit 32 transfers the data output command to the NAND chip 42.Then, the read data is transferred from the NAND chip 42 to the NAND I/Fcircuit 32.

FIG. 7 is a waveform diagram illustrating an example of the toggleinterface according to the embodiment. In the toggle interface accordingto the embodiment, either a first mode or a second mode may be selectedfor transfer of a command and an address. According to the first mode,the same operation as a conventional toggle interface is performed. Thatis, the NAND I/F circuit 32 asserts the command latch enable signal lineCLE and transfers a command to the input/output circuit 102 by the I/Osignal lines DQ [7:0] in synchronization with the rising edge(deasserting) of the write enable signal line WEn. The NAND I/F circuit32 asserts the address latch enable signal line ALE and transfers anaddress to the input/output circuit 102 by the I/O signal lines DQ [7:0]in synchronization with the rising edge (deasserting) of the writeenable signal line WEn. According to the second operation mode, acommand and an address are transferred by two signal lines which are thecommand latch enable signal line CLE and the address latch enable signalline ALE.

In the conventional toggle interface, both the command latch enablesignal line CLE and the address latch enable signal line ALE are at thelow level (deasserted state) during data transfer. Therefore, in thesecond mode, it is possible to transfer a command and an address duringthe data transfer by the two signal lines CLE and ALE. The first modemay be referred to as a toggle interface, and the second mode may bereferred to as a two-lines interface.

When no operation mode is explicitly selected for transfer of a commandand an address, the first mode is performed. Therefore, as illustratedin FIG. 7, the write command is transferred in a similar manner to in acase of the conventional toggle interface illustrated in FIG. 3. In FIG.7, the command 01 h is not illustrated.

The NAND I/F circuit 32 asserts the chip enable signal line CEn and thewrite enable signal line WEn.

The NAND I/F circuit 32 maintains the asserted state of the data strobesignal line DQS/DQSn.

The NAND I/F circuit 32 asserts the command latch enable signal line CLEand deasserts the write enable signal line WEn. The NAND I/F circuit 32transfers the command 80 h to the NAND chip 42 by the I/O signal linesDQ [7:0] in synchronization with the rising edge (deasserting) of thewrite enable signal line WEn.

After transferring the command 80 h, the NAND I/F circuit 32 deassertsthe command latch enable signal line CLE and asserts the address latchenable signal line ALE. The NAND I/F circuit 32 starts periodicasserting/deasserting of the write enable signal line WEn.

The NAND I/F circuit 32 sequentially transfers column addresses C1 andC2 of two cycles and row addresses R1, R2, and R3 of three cycles to theNAND chip 42 by the I/O signal lines DQ [7:0], in synchronization withthe rising edge (deasserting) of the write enable signal line WEn.

After transferring the row address R3, the NAND I/F circuit 32 maintainsthe deasserted state of the write enable signal line WEn to stop theperiodic asserting/deasserting of the write enable signal line WEn.

The NAND I/F circuit 32 deasserts the address latch enable signal lineALE.

The NAND I/F circuit 32 deasserts the data strobe signal line DQS/DQSn.

The NAND I/F circuit 32 starts periodic asserting/deasserting of thedata strobe signal line DQS/DQSn. The NAND I/F circuit 32 sequentiallytransfers write data to the NAND chip 42 by the I/O signal lines DQ[7:0] in synchronization with both the rising edge (asserting) and thefalling edge (deasserting) of the data strobe signal line DQS/DQSn.

It is assumed that, before or during transfer of write data, the readrequest is issued for a NAND chip other than a NAND chip 42 to which thewrite data is transferred or for a NAND chip of another plane of thesame chip. In this case, it is not possible to transfer a read datacommand, a data output command, and an address related to the readrequest, in the first mode. Thus, the NAND I/F circuit 32 changes theoperation mode from the first mode to the second mode (in FIG. 7,referred to as a two-lines mode Entry). The NAND I/F circuit 32 firstasserts the address latch enable signal line ALE and then asserts thecommand latch enable signal line CLE, thereby transferring anotification of the two-lines mode Entry to the NAND chip 42 (peripheralcircuit 44). When detecting the two-lines mode Entry in which theaddress latch enable signal line ALE is first asserted and then thecommand latch enable signal line CLE is asserted, the peripheral circuit44 changes the operation mode from the first mode to the second mode.

After switching to the second operation mode is completed, the NAND I/Fcircuit 32 transfers 1-bit data indicative of a command or an address bythe address latch enable signal line ALE at the falling edge(deasserting) of the command latch enable signal line CLE. The logiccontrol circuit 104 of the peripheral circuit 44 in the NAND chip 42latches data of the address latch enable signal line ALE at the fallingedge (deasserting) of the command latch enable signal line CLE, andsupplies the latched data to the input/output circuit 102. Whenoperating in the second mode, the input/output circuit 102 considers thedata supplied from the logic control circuit 104 as the data input bythe I/O signal lines DQ [7:0].

In the second mode, it is required that the NAND I/F circuit 32 changesthe level of data to be transferred by the address latch enable signalline ALE (from the low level to the high level and from the high levelto the low level) when the command latch enable signal line CLE is atthe high level. Therefore, the NAND I/F circuit 32 sets (asserts) thecommand latch enable signal line CLE to be at the high level, beforechanging the level of the data to be transferred. As described above,data indicative of the command or the address is serially transferred bythe two-lines interface.

The NAND I/F circuit 32 maintains the deasserted state of the writeenable signal line WEn even though the operation mode is switched to thesecond mode.

In the two-lines interface, the command latch enable signal line CLEacts as a clock. The NAND I/F circuit 32 periodically deasserts/assertsthe command latch enable signal line CLE based on a clock generated by abuilt-in oscillator.

When the transfer of the data indicative of the command or the addressis completed, the NAND I/F circuit 32 changes the operation mode fromthe second operation mode to the first operation mode (in FIG. 7,referred to as the two-lines mode Exit). The NAND I/F circuit 32 firstdeasserts the command latch enable signal line CLE and then deassertsthe address latch enable signal line ALE, thereby transferring anotification of the two-lines mode Exit to the NAND chip 42 (peripheralcircuit 44). When the last transferred bit is at the low level (addresslatch enable signal line ALE is in the deasserted state), the NAND I/Fcircuit 32 asserts the address latch enable signal line ALE once beforethe two-lines mode Exit, and then deasserts the address latch enablesignal line ALE.

When detecting the two-lines mode Exit in which the command latch enablesignal line CLE is first deasserted and then the address latch enablesignal line ALE is deasserted, the peripheral circuit 44 changes theoperation mode from the second mode to the first mode. The timing of thetwo-lines mode Exit may be during the transfer of the write data. Whenthe two-lines mode Exit occurs during the transfer of the write data,and another read request is issued, the NAND I/F circuit 32 may changethe operation mode from the first mode to the second mode again andtransfer the command and the address in the second mode.

FIG. 8 illustrates an example of serial transfer according to theembodiment. FIG. 8 is a waveform diagram when 1-bit data indicative ofthe read data command are serially transferred by the two-linesinterface.

In the toggle interface, the level of the command latch enable signalline CLE and the level of the address latch enable signal line ALEindicate whether the transferred byte is a command or an address. Whenthe transferred byte is a command, the level of the command latch enablesignal line CLE is at the high level. When the transferred byte is anaddress, the level of the address latch enable signal line ALE is at thehigh level. There are two combinations of levels of the command latchenable signal line CLE and the address latch enable signal line ALE:(CLE, ALE)=(1, 0) or (CLE, ALE)=(0, 1).

The two-lines interface uses the command latch enable signal line CLEand the address latch enable signal line ALE are used for command oraddress transfer. Therefore, the level of the command latch enablesignal line CLE and the level of the address latch enable signal lineALE cannot indicate whether the transferred byte is a command or anaddress. In the two-lines interface, it is necessary to transfer anadditional determination bit indicative of whether (CLE, ALE)=(1, 0) or(CLE, ALE)=(0, 1). For example, the NAND I/F circuit 32 adds the 1-bitdetermination bit to the transfer byte. The determination bit may beadded before and after the transfer byte or at any position within thetransfer byte. In the example in FIG. 8, the NAND I/F circuit 32 addsthe determination bit “ca” before the transfer byte. Since the logiccontrol circuit 104 latches the address latch enable signal line ALE atthe falling edge of the command latch enable signal line CLE, thefalling edge of the command latch enable signal line CLE corresponds tothe determination bit “ca”. The determination bit “ca”=0 indicates that(CLE, ALE)=(1, 0) and the transfer byte is a command. The determinationbit “ca”=1 indicates that (CLE, ALE)=(0, 1), and the transfer byte is anaddress.

As illustrated in FIG. 4, it is assumed that the read data command is a7-byte command from the command 00 h to the command 30 h. In FIG. 8, thecommand 01 h/02 h/03 h is not illustrated. In order to serially transferthe 7-byte read data command, it is necessary to serially transfer 63(=(8+1)×7) bits. Since the byte immediately after the two-lines modeEntry is indicative of the command 00 h, “ca”=0. From the next byte, anaddress is transferred. Therefore, “ca”=1. The last byte is indicativeof the command 30 h. Therefore, “ca”=0.

The transfer speed of the two-lines interface depends on thedeasserting/asserting frequency of the command latch enable signal lineCLE. When the command latch enable signal line CLE repeats thedeasserting/asserting at 100 MHz, the time to transfer one read datacommand is 630 ns and two-lines mode Entry/Exit time. The two-lines modeEntry/Exit time is sufficiently smaller than 3.96 μs being the datatransfer time of one page (command transfer disabled time) in the toggleinterface with a data transfer speed of 4.8 Gbps. Thus, during the datatransfer, it is possible to perform serial communication of a commandand an address by the two-lines interface. In addition, it is possibleto improve the performance of the SSD 14.

FIG. 9 illustrates the state in which the four NAND chips 42-0 to 42-3are connected to the memory controller 20. By the two-lines interface inthe embodiment, for example, when write data is transferred to the NANDchip 42-2 by the I/O signal lines DQ [7:0], it is possible to transfer acommand and an address to the NAND chip 42-2 or other NAND chips (42-0,42-1, 42-3) by the command latch enable signal line CLE and the addresslatch enable signal line ALE which are fixed in the toggle interface.Similarly, when a command and an address are transferred to any NANDchip 42 by the I/O signal lines DQ [7:0], it is possible to transferdata to any NAND chip 42 by the command latch enable signal line CLE andthe address latch enable signal line ALE.

As the embodiment, the case where the read request is issued during thetransfer of the write data after the write command is issued has beendescribed. The embodiment can be similarly applied to other cases. Forexample, the embodiment can be applied to a case where another writerequest is issued during the transfer of write data, a case where thewrite request is issued during the transfer of read data, and a casewhere another read request is issued during the transfer of the readdata.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions, and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An electronic apparatus comprising: an interfacecircuit connectable to a first signal line, a second signal line, and athird signal line; and a controller configured to transmit a firstcommand, a first address, data, and one of a second address and a secondaddress via the interface circuit, wherein before transmitting the datausing the first signal line, the controller is configured to transmitthe first command using the first signal line while transmitting a firstcontrol signal using the second signal line, and transmit the firstaddress using the first signal line while transmitting a second controlsignal using the third signal line, and while transmitting the datausing the first signal line, the controller is configured to transmit atleast one of the second command and the second address using the secondsignal line and the third signal line.
 2. The electronic apparatus ofclaim 1, wherein the controller is configured to assert the secondsignal line while the third signal line is asserted, and transmit atleast one of the second command and the second address after assertingthe second signal line.
 3. The electronic apparatus of claim 2, whereinthe controller is configured to periodically deassert and assert thesecond signal line after asserting the second signal line, and transmitat least one of the second command and the second address upon at leastone of asserting the second signal line and deasserting the secondsignal line.
 4. The electronic apparatus of claim 3, wherein thecontroller is configured to change a level of the third signal linewithin an assert period of the second signal line while transmitting atleast one of the second command and the second address.
 5. The memorysystem of claim 6, wherein while transmitting the data using the firstsignal line, when the third signal line is deasserted after transmittingat least one of the second command and the second address, thecontroller is configured to assert the third signal line, deassert thesecond signal line after asserting the third signal line, and deassertthe third signal line after deasserting the second signal line, andwhile transmitting the data using the first signal line, when the thirdsignal line is asserted after transmitting at least one of the secondcommand and the second address, the controller is configured to deassertthe second signal line, and deassert the third signal line afterdeasserting the second signal line.
 6. A memory system comprising: anonvolatile memory; a first signal line connected to the nonvolatilememory; a second signal line connected to the nonvolatile memory; athird signal line connected to the nonvolatile memory; and a controlcircuit, wherein the control circuit comprises: an interface circuitconnected to the first signal line, the second signal line, and thethird signal line; and a controller configured to transmit a firstcommand, a first address, data, and one of a second address and a secondaddress to the nonvolatile memory via the interface circuit, beforetransmitting the data using the first signal line, the controller isconfigured to transmit the first command using the first signal linewhile transmitting a first control signal using the second signal line,and transmit the first address using the first signal line whiletransmitting a second control signal using the third signal line, andwhile transmitting the data using the first signal line, the controlleris configured to transmit at least one of the second command and thesecond address using the second signal line and the third signal line.7. The memory system of claim 6, wherein the controller is configured toassert the second signal line while the third signal line is asserted,and transmit at least one of the second command and the second addressafter asserting the second signal line.
 8. The memory system of claim 7,wherein the controller is configured to periodically deassert and assertthe second signal line after asserting the second signal line, andtransmit at least one of the second command and the second address uponat least one of asserting the second signal line and deasserting thesecond signal line.
 9. The memory system of claim 8, wherein thecontroller is configured to change a level of the third signal linewithin an assert period of the second signal line while transmitting atleast one of the second command and the second address.
 10. The memorysystem of claim 6, wherein while transmitting the data using the firstsignal line, when the third signal line is deasserted after transmittingat least one of the second command and the second address, thecontroller is configured to assert the third signal line, deassert thesecond signal line after asserting the third signal line, and deassertthe third signal line after deasserting the second signal line, andwhile transmitting the data using the first signal line, when the thirdsignal line is asserted after transmitting at least one of the secondcommand and the second address, the controller is configured to deassertthe second signal line, and deassert the third signal line afterdeasserting the second signal line.
 11. A transfer method fortransferring a first command, a first address, data, and one of a secondaddress and a second address between a nonvolatile memory and acontroller, the method comprising: before transferring the data usingthe first signal line, transferring the first command using the firstsignal line while transferring a first control signal using the secondsignal line, and transferring the first address using the first signalline while transferring a second control signal using the third signalline, and while transferring the data using the first signal line,transferring at least one of the second command and the second addressusing the second signal line and the third signal line.